Remove the blocking for the original water pipes (Image 1).
Measure the distance between the studs so that you will have a tight fit for your supports.
After the stringers have been cut, pre-drill them so they will be easier to install (Image 2).
Set them in place between the studs. Make sure they line up with the holes you pre-drilled for them through the tile. Secure them to the wall studs with wood screws. These 2 stringers are what your lag bolts will attach to when you are ready to mount the shower unit to the wall (Image 3).
There are a variety of multi-head shower units on the market. Check your manufacturer's instructions before beginning any installation.
Place some duct tape around the supply lines in the back of the shower wall.
Inside the shower, fill the areas around the pipes with silicone. The duct tape keeps you from filling up the entire wall. The silicone will seal up the holes and block any water that may run between the shower unit and the wall.
With the wall studs now reinforced to handle the weight of the shower, and the holes for the new water lines sealed up, you are ready to install the new shower system and hook the water back up.
You need to pre-drill the holes in the stringers so your lag bolts will go in.
Fill the holes with silicone so the excess will seal up around the bolts once they are screwed into place.
Lift the shower unit over the supply lines and line up the holes for the bolts. Shim it again to raise it the required distance off the basin floor.
Attach the unit to the wall using a 1/2" socket wrench to secure the bolts into the stringers. Then, remove the shim from underneath.
Use "thread sealant" at the supply lines to prevent any leaks.
Install the water hoses inside the unit to the new lines.
Turn the water main on and bleed the lines at the shower.
Napkins work well to check the fittings for any possible leaks. Check the fittings in the shower and in the wall where you ran the new supply lines.
Attach the hose for the spray handle, and then place the cover back on the shower base.
Replace the cylinder over the water valve of the unit, and screw the top plate to the valve.
Install a rubber gasket on the outside of the valve cover and install a small plastic pin in the face of the cover plate.
Install the finish trim plate to the cover plate. The finish trim piece will snap onto the cover plate.
Install the covers for the faucet controls.
Unscrew the top of the showerhead, and then screw the finish trim on.
Hook up all of the nozzles and sprays on the face of the unit.
A multi-nozzle shower uses more hot water than a standard single-head unit. Before you buy and install any multi-head shower, find out if your water heater can handle the additional demand.